Energy evolution varies during the whole process of rock deformation, and mechanical parameters are markedly altered under cyclic loading and unloading. In order to investigate the effects of confining pressure on energy evolution and mechanical parameters, cyclic loading and unloading experiments were performed for granite under six different confining pressures. The experiment revealed the confining pressure effect on variation and allocation pattern of energy and mechanical characteristics. Four characteristic energy parameters, namely, storage energy rock, storage energy limit, energy storage ratio, and energy dissipation ratio, were proposed to describe energy storage and dissipation properties of rock. Elastic modulus and dissipation ratio presented a downward “U” and “U”-shaped trends, respectively, with loading and unloading cycles, while Poisson’s ratio increased linearly at the same time. Elastic energy was accumulated mainly before peak stress, while the energy dissipation and release were dominant after the peak strength. As the confining pressure increased, efficiency of energy accumulation and storage limit improved. An exponential function was proposed to express the relationship between the energy storage limit and confining pressure. Dissipation energy increased nonlinearly with the strain, and the volume dilatancy point defined the turning point from a relatively slow growth to an accelerated growth of dissipation energy. The dilatancy point can be used as an important indication for the rapid development of dissipation energy.
During the microstructural analysis of weakly cemented sandstone, the granule components and ductile structural parts of the sandstone are typically generalized. Considering the contact between granules in the microstructure of weakly cemented sandstone, three basic units can be determined: regular tetrahedra, regular hexahedra, and regular octahedra. Renormalization group models with granule-and pore-centered weakly cemented sandstone were established, and, according to the renormalization group transformation rule, the critical stress threshold of damage was calculated. The results show that the renormalization model using regular octahedra as the basic units has the highest critical stress threshold. The threshold obtained by iterative calculations of the granule-centered model is smaller than that obtained by the pore-centered model. The granule-centered calculation provides the lower limit (18.12%), and the pore-centered model provides the upper limit (36.36%). Within this range, the weakly cemented sandstone is in a phase-like critical state. That is, the state of granule aggregation transforms from continuous to discrete. In the relative stress range of 18.12%-36.36%, the weakly cemented sandstone exhibits an increased proportion of high-frequency signals (by 83.3%) and a decreased proportion of low-frequency signals (by 23.6%). The renormalization calculation results for weakly cemented sandstone explain the high-low frequency conversion of acoustic emission signals during loading. The research reported in this paper has important significance for elucidating the damage mechanism of weakly cemented sandstone.
Inorganic nanomaterials such as graphene, black phosphorus,
and
transition metal dichalcogenides have attracted great interest in
developing optoelectronic devices due to their efficient conversion
between light and electric signals. However, the zero band gap nature,
the unstable chemical properties, and the low electron mobility constrained
their wide applications. Bismuth oxyselenide (Bi2O2Se) is gradually showing great research significance in the
optoelectronic field. Here, we develop a bismuth oxyselenide/p-silicon
(Bi2O2Se/p-Si) heterojunction and design a self-powered
and broadband Bi2O2Se/p-Si heterojunction photodetector
with an ultrafast response (2.6 μs) and low dark current (10–10 A without gate voltage regulation). It possesses
a remarkable detectivity of 4.43 × 1012 cm Hz1/2 W–1 and a self-powered photoresponse
characteristic at 365–1550 nm (ultraviolet-near-infrared).
Meanwhile, the Bi2O2Se/p-Si heterojunction photodetector
also shows high stability and repeatability. It is expected that the
proposed Bi2O2Se/p-Si heterojunction photodetector
will expand the applications of Bi2O2Se in practical
integrated circuits in the field of material science, energy development,
optical imaging, biomedicine, and other applications.
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